High Electron Mobility Transistors are known to be desirable in certain applications. One such application is microwave amplifiers. They are known to generally yield higher output power densities, lower noise figures, and be able to operate at higher frequencies as compared to other Field Effect Transistors (FETs). GaN material system based HEMT's are believed to be desirable for use in Radio Frequency (RF) modulation schemes and interfaces.
However, drain current reduction at high frequencies has conventionally limited the available output power in GaN material system-based HEMT devices, which is believed to be caused by the surface states. It is believed desirable to passivate the surface states and prevent surface damage during device processing. Low breakdown voltage has conventionally limited high drain biases for GaN material system based HEMT devices. It is believed desirable to increase the breakdown voltage. Further, the power performance of conventional GaN material system based HEMT devices typically degrades at high junction temperatures, due to reduced carrier saturation velocity and increased parasitic resistance. It is believed to be desirable to maintain a high two dimensional electron gas (2 DEG) mobility even at high temperatures. Repeatable low contact resistance in conventional GaN material system based HEMT devices has also proven problematic for high frequency operation. It is believed desirable to provide for repeatable and low contact resistances. It is also believed to be desirable to increase the 2 DEG sheet charge and maintain 2 DEG confinement to increase usable RF power and eliminate drain current reduction at high frequencies.